The Democratic Congressional Campaign Committee on Monday is naming 19 members to the Frontline Program for its most vulnerable incumbents in 2018.

The initial Frontline roster, obtained first by Roll Call, is about half freshman members. Eight members won in districts President Donald Trump carried last fall. And all of them, save for one, are National Republican Congressional Committee initial targets.

Rep.-elect Ruben Kihuen, D-Nev., delivers his victory speech flanked by his family and supporters at the Nevada Democrats' election night watch party at the Aria Hotel and Resort in Las Vegas on Election Day. (Photo By Bill Clark/CQ Roll Call)

Not all districts are created equal. They all count the same when adding for a majority, but victories in one type of district may portend a much better night for Democrats than in others. With just four days to go until Election Day, Democrats almost surely won’t gain the 30 seats needed for a House majority on Tuesday. But they will make some gains. Here’s where to watch for early clues as to just how big or small Democratic gains will be.

To achieve double-digit gains, Democrats must win the known battlegrounds. These are the districts that always were going to be competitive, and where presidential year turnout usually gives Democrats an advantage. At the very least, Democrats need to win the districts that President Barack Obama carried — places like Illinois’ 10th District, Nevada’s 4th and 3rd Districts, Maine’s 2nd District, Florida’s 26th District, (which is now even more Democratic), Iowa’s 1st District and New York’s 19th District. If they’re not able to win these seats, Democratic gains in the House will likely be very minimal.

President Barack Obama continued a Democratic full-court press on down-ballot Republicans, campaigning and cutting ads in key Senate and House races.

Holding a solid lead over Republican Donald Trump, Hillary Clinton has also turned her attention to those races, too. She will likely give some aid to North Carolina Senate challenger Deborah Ross when she campaigns in Winston-Salem with Michelle Obama on Thursday.

The Congressional Leadership Fund, a super PAC backed by House Republican leadership, is pouring another $10.7 million into House races as the GOP seeks to defend their hold on the lower chamber and flip several Democratic-held seats.

The additional spending brings the fund's general election expenditures this cycle to $20.7 million in 15 House districts, nearly twice what it spent in 2014 and 2012. The super PAC spent $11.6 million in 2014 and $10.7 million in 2012.